We describe trends in occupational and nonoccupational injury among working-age adults in Ontario. We conducted an observational study of adults aged 15 to 64 over the period 2004 through 2011, estimating the incidence of occupational and nonoccupational injury from emergency department (ED) records and, separately, from survey responses to 5 waves of a national health interview survey. Over the observation period, the annual percentage change (APC) in the incidence of work-related injury was -5.9% (95% confidence interval [CI] = -7.3, -4.6) in ED records and -7.4% (95% CI=-11.1, -3.5) among survey participants. In contrast, the APC in the incidence of nonoccupational injury was -0.3% (95% CI=-0.4, 0.0) in ED records and 1.0% (95% CI=0.4, 1.6) among survey participants. Among working-age adults, the percentage of all injuries attributed to work exposures declined from 20.0% in 2004 to 15.2% in 2011 in ED records and from 27.7% in 2001 to 16.9% in 2010 among survey participants. Among working-age adults in Ontario, nearly all of the observed decline in injury incidence over the period 2004 through 2011 is attributed to reductions in occupational injury.